Selective etch using material modification and RF pulsing

ABSTRACT

Semiconductor systems and methods may include methods of performing selective etches that include modifying a material on a semiconductor substrate. The substrate may have at least two exposed materials on a surface of the semiconductor substrate. The methods may include forming a low-power plasma within a processing chamber housing the semiconductor substrate. The low-power plasma may be a radio-frequency (“RF”) plasma, which may be at least partially formed by an RF bias power operating between about 10 W and about 100 W in embodiments. The RF bias power may also be pulsed at a frequency below about 5,000 Hz. The methods may also include etching one of the at least two exposed materials on the surface of the semiconductor substrate at a higher etch rate than a second of the at least two exposed materials on the surface of the semiconductor substrate.

TECHNICAL FIELD

The present technology relates to systems and methods for processingsemiconductor materials. More specifically, the present technologyrelates to semiconductor material modifications and hardwaremodifications for producing a low-power plasma.

BACKGROUND

Integrated circuits are made possible by processes which produceintricately patterned material layers on substrate surfaces. Producingpatterned material on a substrate requires controlled methods forapplying and removing material. For removal, chemical etching is usedfor a variety of purposes including transferring a pattern inphotoresist into underlying layers, thinning layers, or thinning lateraldimensions of features already present on the surface. Often it isdesirable to have an etch process that etches one material faster thananother facilitating, for example, a pattern transfer process. Such anetch process is said to be selective to the first material. As a resultof the diversity of materials, circuits, and processes, etch processeshave been developed with a selectivity towards a variety of materials.

Etch processes may be termed wet or dry based on the materials used inthe process. A wet HF etch preferentially removes silicon oxide overother dielectrics and materials. However, wet processes may havedifficulty penetrating some constrained trenches and also may sometimesdeform the remaining material. Dry etches produced in local plasmasformed within the substrate processing region can penetrate moreconstrained trenches and exhibit less deformation of delicate remainingstructures. However, local plasmas may damage the substrate through theproduction of electric arcs as they discharge. Additionally, plasmaeffluents can damage chamber components that may require replacement ortreatment.

Thus, there is a need for improved systems and methods that can be usedto produce high quality devices and structures. These and other needsare addressed by the present technology.

SUMMARY

Semiconductor systems and methods may include methods of performingselective etches that include modifying a material on a semiconductorsubstrate. The substrate may have at least two exposed materials on asurface of the semiconductor substrate. The methods may include forminga low-power plasma within a processing chamber housing the semiconductorsubstrate. The low-power plasma may be a radio-frequency (“RF”) plasma,which may be at least partially formed by an RF bias power operatingbetween about 10 W and about 100 W in embodiments. The RF bias power mayalso be pulsed at a frequency below about 5,000 Hz. The methods may alsoinclude etching one of the at least two exposed materials on the surfaceof the semiconductor substrate at a higher etch rate than a second ofthe at least two exposed materials on the surface of the semiconductorsubstrate.

In embodiments the modifying operation may include forming a plasma froma precursor within the processing chamber with the RF bias power. Theprecursor may be selected from the group consisting of oxygen, hydrogen,or helium in embodiments. Additionally, each of the at least two exposedmaterials on the surface of the semiconductor substrate may be selectedfrom the group consisting of silicon oxide, silicon nitride, siliconcarbide, and silicon oxycarbide.

For the etching operation, the RF bias power may at least partially formthe low-power plasma and operate at a duty cycle below about 50%. Also,forming the low-power plasma may further include utilizing an RF sourcepower below about 100 W. In embodiments, forming the low-power plasmamay also include utilizing a pulsed DC power. The pulsed DC power may beapplied to a bipolar electrostatic chuck supporting the semiconductorsubstrate. In embodiments, the pulsed DC power may be applied to aconductive ring embedded in a shield ring of a pedestal supporting thesemiconductor substrate or coupled with a showerhead within theprocessing chamber.

The present technology also includes methods of removing material from asemiconductor substrate. The methods may include modifying a material ona semiconductor substrate having at least two exposed materials on asurface of the semiconductor substrate. The modifying may includeforming a plasma from a precursor with an RF bias power to generateplasma effluents that modify the material. The methods may also includeforming a low-power plasma within a processing chamber housing thesemiconductor substrate. The low-power plasma may be a radio-frequency(RF) plasma in embodiments. The low-power plasma may be formed by apulsed RF bias power operating at between about 20 W and 50 W at apulsing frequency between about 500 Hz and about 2,000 Hz. The pulsed RFbias power may be operated at a duty cycle of between about 20% and 50%as well. The methods may include operating a DC pulsed power on analternating frequency with the RF bias power pulsing. The methods mayfurther include etching one of the at least two exposed materials on thesurface of the semiconductor substrate at a selectivity of at leastabout 20:1 with respect to a second of the at least two exposedmaterials on the surface of the semiconductor substrate.

In the methods, the modifying operation may include a chemicalmodification causing a chemical change to the material on thesemiconductor substrate. The modifying may also include a physicalmodification utilizing an inert precursor. In embodiments, the physicalmodification may include damaging bonds of the material on thesemiconductor substrate with ions of the inert precursor. The formingthe low-power plasma operation may further include utilizing an RFsource power operating up to about 100 W.

The present technology also includes substrate processing chambersincluding a pedestal configured to support a semiconductor substrate.The chambers may include an RF bias power electrically coupled with thepedestal and configured to generate a plasma within the processingchamber at a power of between about 20 W and about 50 W in embodiments.The RF bias power may be a pulsing power configured to pulse at afrequency below about 5,000 Hz. The substrate processing chambers mayfurther include a DC pulsing power electrically coupled with thesubstrate processing chamber and configured to produce priming particlesfor the RF bias plasma. Additionally, the DC pulsing power supply may beconfigured to pulse at a frequency to produce priming particles withoutdeveloping a plasma sheath.

In embodiments, the DC pulsing power supply may be configured to bepulsed on for a duration of 100 microseconds or less at a duty cycle ofless than about 50%. Additionally, in embodiments the pedestal may be abipolar electrostatic chuck, and the DC pulsing power may be applied toelectrical ground of the bipolar electrostatic chuck. In embodiments theDC pulsing power may be electrically coupled with a conductive ringcoupled with the pedestal, and the conductive ring may be electricallydecoupled from the electrostatic chuck and the RF bias. In embodimentsthe DC pulsing power may also be electrically coupled with a conductivering embedded in a showerhead within the substrate processing chamber.

Such technology may provide numerous benefits over conventionaltechniques. For example, the technology may allow improved selectivityof etching operations due to, for example, the material modifications.Additionally, the low-power plasmas of the present technology mayproduce improved feature profiles over conventional techniques, andallow improved front end and back end processing with enhanced plasmacontrol. These and other embodiments, along with many of theiradvantages and features, are described in more detail in conjunctionwith the below description and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the disclosedembodiments may be realized by reference to the remaining portions ofthe specification and the drawings.

FIG. 1 illustrates a method of etching a substrate according toembodiments of the present technology.

FIG. 2 shows a graph illustrating the additive effects of materialmodification and low-power plasma according to embodiments of thepresent technology.

FIG. 3 shows imaging of an etch process performed according toembodiments of the present technology.

FIG. 4 shows a chart illustrating etch rates of various materials withand without treatments according to embodiments of the presenttechnology.

FIG. 5 shows a chart illustrating etch rates of silicon oxycarbide andsilicon carbide with and without treatments according to embodiments ofthe present technology.

FIG. 6 shows a partial schematic illustration of a controller providingDC pulse to an electrostatic chuck according to embodiments of thepresent technology.

FIG. 7 shows a partial schematic illustration of a controller providingDC pulse to a conductor coupled with a pedestal structure within aprocessing chamber according to embodiments of the present technology.

FIG. 8 shows a partial schematic illustration of a controller providingDC pulse to a conductor coupled with a showerhead of a processingchamber according to embodiments of the present technology.

In the appended figures, similar components and/or features may have thesame numerical reference label. Further, various components of the sametype may be distinguished by following the reference label by a letterthat distinguishes among the similar components and/or features. If onlythe first numerical reference label is used in the specification, thedescription is applicable to any one of the similar components and/orfeatures having the same first numerical reference label irrespective ofthe letter suffix.

DETAILED DESCRIPTION

In semiconductor processing, etching may be performed for a number ofreasons. In dry etching, precursors may be flowed through plasma toproduce radical plasma effluents for etching various semiconductormaterials. The plasma effluents include ions directed to the surface ofthe substrate and materials to be etched. In certain etching operations,such as with reactive-ion etching, the ions are directed to the surfaceof the materials, and based on the energy involved can sputter thematerials from the surface of the substrate. Other etching operationsare designed with a goal towards removing one material faster than asecond material, often called a selective etch. In order to enhanceselectivity, one approach may include reducing the sputtering componentof an etching operation. This may be achieved in part by reducing theplasma power in order to reduce the electron temperature. Selectivitymay become increasingly critical as feature size reduces. The higher theselectivity, the less material that is meant to be maintained may beformed as a buffer for the target dimensions of the final product. Evenconventionally higher selectivities may be unsuitable as feature sizescontinue to reduce. For example, if even a few nanometers is removedfrom materials meant to be maintained, device performance may benegatively impacted.

Plasma may be produced in a number of ways including, for example, witha radio-frequency (“RF”) bias electrically connected to a pedestalsupporting a substrate. This bias power may be used in conjunction withor alternatively to an RF source coupled with portions of the chamber,or may work in conjunction with an inductively-coupled plasma source, acapactively-coupled plasma source, a microwave source, or any otherplasma source that may additionally be used to produce plasma effluents.By utilizing a bias power in lieu of or in addition to a source power,directionality may be provided to the ions to provide more of ananisotropic, or orientation dependent etch. However, as ion energyincreases, sputtering may also increase. Because sputtering may be morematerial independent, it can reduce selectivity between materials whereonly one is desired to be removed. Accordingly, a goal may be to reducethe plasma power on bias to reduce sputtering in an attempt to improveselectivity.

Conventional technologies may reduce the plasma power at the source orthe bias, but are limited in the degree to which the bias power may bereduced both from the perspective of striking a plasma as well as inproducing an etch. In order to strike a plasma, the power must exceedthe breakdown voltage of the fluid from which plasma is produced. Forconventional sputtering and pulsed-etch operations, glow discharge isoften produced around, for example, 500 V and at a power of severalthousand Watts in a low current, medium voltage regime. These powerlevels, however, will provide increased ion energy and concomitantsputtering of materials, which may lead to lower selectivity. If plasmapower is lowered to further reduce sputtering, it may be difficult togenerate or sustain a plasma at all, especially with a pulsed plasmapower. Additionally, if the bias power is reduced too far, althoughsputtering may be resolved, overall etching may be reduced to zero.

The present technology overcomes many of these issues by producing alow-power RF plasma that is pulsed. Conventional so-called low-powerplasmas may be produced at up to a few hundred Watts of source power andat a pulsing frequency in the megahertz range. These power ranges areunable to produce the selectivities of the present technology becausethe sputtering component of these plamsas is still too pronounced. Thepresent technology, on the other hand, may produce plasmas at a varietyof chamber conditions with a pulsed RF bias operating below 100 Watts,at a duty cycle down to about 20%, and at a pulsing frequency down toabout 500 Hz. In this operating regime, sputtering may be reduced orsubstantially eliminated and etch selectivies may be produced that maybe up to an order of magnitude improvement over conventionaltechnologies. The present technology may involve a combination ofenhancing selectivity via material modification and performing alow-power etch. These processes may enhance overall selectivity byreducing the amount of materials meant to be maintained both by reducingthe amount etched in relation to other materials, as well as by reducingany plasma effects that may sputter or impact the materials negatively.

Although the following description will routinely identify etchingoperations, it is to be understood that the techniques may be appliedmore broadly. The system and operating methods may additionally byapplied to deposition, cleaning, or any other plasma operations that maybenefit from a low-power plasma as described. Accordingly, thedescription is not intended to limit the applications only to theexamples described throughout the specification.

FIG. 1 illustrates a method 100 of etching a substrate according toembodiments of the present technology. Optional operations may beperformed prior to the noted method operations including patterning,film formation, or a variety of other known process operations. Themethod may include modifying a material on a semiconductor substrate atoperation 110. The substrate may have at least two exposed materials ona surface of the semiconductor substrate, and may have three, four,five, six, or more different materials exposed. Additionally, one ormore materials may be initially covered prior to the selective etchingmethod 100 but then exposed by the operations, and thus one or more ofthe exposed films may be exposed during the etching operation inembodiments. In embodiments, removal of one or more of these materialsmay be sought.

The method may also include forming a low-power plasma within aprocessing chamber housing the semiconductor substrate at operation 120.The low-power plasma may be a radio-frequency (“RF”) plasma inembodiments, although other plasma formations may similarly beencompassed. The low-power plasma may be at least partially formed by anRF bias power operating at between about 10 W and 100 W in embodiments.The RF bias power may be pulsed, and may be operated at a pulsingfrequency below about 5,000 Hz in embodiments. The method may furtherinclude etching one or more of the at least two exposed materials on thesurface of the semiconductor substrate at operation 130. The etching ofone or more of the at least two exposed materials may be at a higherrate than a second of the at least two exposed materials on the surfaceof the semiconductor substrate in embodiments.

The modifying operation may be tuned in any number of ways based on thematerials on the surface of the substrate, and may be based on anidentification of properties of the materials and how they may differfrom other materials on the substrate surface. For example, themodifying operations may initially identify differences in density,chemical structure, reactive nature, or any other characteristicsbetween films that may be utilized. The modification to one or more ofthe materials may be performed to enhance or produce differences betweenthe films that may be exploited in an etching operation. Themodification may be performed in embodiments by exposing the materialsto one or more precursors. In embodiments, the precursors may or may notbe excited prior to interacting with the exposed materials. Inembodiments, the modifying may include forming a plasma from a precursorwithin the processing chamber. The plasma may be from between about 50 Wto about 300 W depending on the film being modified. For example, filmsexhibiting a higher density may benefit from a higher plasma power inembodiments. The plasma may be produced with a source power or a biaspower in embodiments, as well as with a combination of the two in orderto generate plasma effluents that modify one or more of the exposedmaterials. In embodiments, the plasma may be formed with an RF biaspower.

The precursor utilized in the operation may include one or moreprecursors based on the type of modification being performed. Theprecursors may include one or more precursors intended to react with thematerials in one form or another, or may include one or more precursorsintended to physically alter one or more of the exposed materials. Acombination of precursors having either or both of these effects mayalso be utilized in embodiments. In examples, the precursors may beselected from the group of elements including noble or inert elements,such as helium, neon, argon, krypton, xenon, and radon. The precursorsmay also be selected from halogens including fluorine, chlorine,bromine, iodine, and astatine, in embodiments. The precursors may alsobe selected from the chalcogens including oxygen, as well as a varietyof other reactive and non-reactive precursors including hydrogen, forexample.

As noted above, the modifying operation may include either or both of achemical modification or a physical modification. A chemicalmodification may cause a chemical change to one or more of the materialson the semiconductor substrate. The chemical change may include areaction such as, for example, producing an oxide of a material layer inembodiments. The chemical change may also adjust bonding structures ofthe materials, or may chemically alter atoms or molecules of thematerial, such as, for example, by removing electrons. The chemicalmodification may also involve densifying a material or film that is tobe maintained on the surface of the substrate in relation to anadditional material to be removed. Physical modification may beperformed with an inert precursor that does not react with exposedmaterials on the substrate. For example, physical modification mayinvolve damaging bonds of one or more of the materials on thesemiconductor substrate with ions of the inert precursor. It is to beunderstood that the modification may involve a combination of chemicaland physical modification, and individual precursors utilized may causean amount of both physical and chemical modification to occur.

The materials on the surface of the semiconductor substrate may includea variety of materials used in various semiconductor processing. Thematerials may include metals, dielectrics, etch stop layers, andsubstrate materials that may include any of a number of elementscommonly understood in semiconductor processing. For example, thematerials may include metals such as copper, tungsten, titanium, orother metals or metal-containing layers. The materials may also includesilicon-containing materials such as silicon oxide, silicon nitride,polysilicon, silicon carbide, silicon oxycarbide, silicon carbonitride,or materials based on other semiconductor base materials, such as, forexample, gallium.

In embodiments, the low-power plasma utilized in the etching operationmay be at least partially produced from an RF bias power electricallycoupled with a pedestal on which the substrate is supported. The biaspower may be operated at a power of from about 1 W to about 500 W inembodiments. The bias power may also be operated from about 10 Watts toabout 250 Watts, from about 15 Watts to about 200 Watts, from about 20Watts to about 150 Watts, from about 20 Watts to about 100 Watts, orfrom about 20 Watts to about 50 Watts in embodiments. The bias power maybe operated in this range which may provide benefits of reducingsputtering, while still striking a plasma and producing etch results.For example, as power levels increase, sputtering may increase as welldue to increased ion energy, and so the power level may be maintainedbelow about 100 Watts in embodiments. On the other hand, the power levelmay be maintained above about 20 Watts in embodiments, as levels belowthis threshold may have reduced etching capacity or ability to strike aplasma. These parameters may also be dependent to a degree on chamberconditions including pressure and temperature, but may still generatestable plasma under pulsing conditions utilizing the technologydiscussed in more detail below.

The RF bias power may be operated at a low duty cycle and pulsingfrequency in order to generate the low-power plasma. The duty cycle maybe below about 75% in embodiments, and may be below about 70%, belowabout 65%, below about 60%, below about 55%, below about 50%, belowabout 45%, below about 40%, below about 35%, below about 30%, belowabout 25%, below about 20%, below about 15%, or below about 10% inembodiments. The RF bias pulsing duty cycle may also be operated with aduty cycle between about 10% and about 60%, or between about 20% and 50%in embodiments for similar reasons of maintaining lower ion energy whilestill having enough on-time to generate stable plasma.

The frequency of pulsing for the RF bias may be below about 10 kHz inembodiments. The frequency of pulsing for the RF bias may also be belowabout 9,000 Hz, below about 8,000 Hz, below about 7,000 Hz, below about6,000 Hz, below about 5,000 Hz, below about 4,500 Hz, below about 4,000Hz, below about 3,500 Hz, below about 3,000 Hz, below about 2,500 Hz,below about 2,000 Hz, below about 1,500 Hz, below about 1,000 Hz, belowabout 750 Hz, or below about 500 Hz in embodiments. The pulsingfrequency may also be maintained between about 500 Hz and about 5,000 Hzin embodiments or about 500 Hz and about 2,000 Hz in embodiments. Thefrequency of the bias pulsing may affect the dissociation of the plasmaprecursors, and thus by adjusting the frequency, the dissociation may beadjusted.

In addition to the RF bias power, an RF source power may be used inembodiments. The RF source power may be used in the etching operationwith a power up to about 1,000 W or less, and may be operated with apower up to about 500 W, or up to about 100 W in embodiments. The RFsource power may be operated below about 100 W in embodiments, and maybe operated between about 0 W and 100 W in embodiments. Differentprecursors may benefit from the addition of RF source, while otherprecursors may benefit from the lack of RF source power. For example, RFsource may increase polymer dissociation, so for certain precursorsincluding, for example C₄F₈ and C₄F₆, source power may dissociate thepolymer and deposit carbon material on the substrate impeding the etchoperation. Accordingly, using a low or no RF source may improve etchingin some embodiments. In embodiments a variety of precursors may beutilized in the etching operation depending on the type of film beingetched. Exemplary precursors that may be used include C₄F₈, C₄F₆, CF₄,Cl₂, CH₂F₂, O₂, N₂, as well as any other precursors that may provideetchant characteristics to remove the target material.

The RF bias conditions previously discussed may pose difficulties incontrolling the plasma sheath or maintaining homogeneity of the sheathin embodiments. However, the conditions may aid in minimizing sputteringduring the etching processes. Accordingly, the present technologyfurther seeks to gain control over operating plasmas at low power thatmay not be assisted by magnetics or associated components. As pressuresand operating conditions are adjusted for particular processes, plasmasmay be more difficult to strike under these conditions. Plasmageneration or gas discharge may in part depend on priming particles orcreating energized particles as a precursor to breakdown. Theseenergized particles are generated to accelerate discharge, which mayreduce the needed firing voltage. During a pulsing power operation suchas that previously discussed, including an additional energy source toproduce priming particles and to maintain electrons in the plasmafeedback loop may aid in the control of plasma generation at low powerduring a variety of processing conditions. By providing the additionalenergy source, plasma may then be struck at low or lower than normalpower levels such as those described above. The present technologyprovides additional sources of energy in embodiments to return energeticparticles back into the plasma priming loop.

A variety of additional energy sources may be utilized in the presenttechnology, and in one example may include a pulsed DC power. The pulsedDC power may be connected to a variety of locations in the chamber inorder to help prime the plasma before the low-power plasma is struckwith the RF bias power. However, this pulsed DC power is fundamentallydifferent from conventional DC bias. In some conventional processing, DCbias is applied in the system, including as a bias on the pedestal. Whenthe DC pulse is applied, the plasma will form all the way from the bulkand will be maintained long enough for current to be accommodated in aplasma sheath at the pedestal. Accordingly, it will collapse down to thesurface of the pedestal creating a sheath with a certain amount of DCpotential. This plasma sheath and potential produces ion energies forthe process and will produce sputtering of the materials at the surfaceof the cathode due to high ion energies associated with the DC plasma.The present technology, however, may cycle the DC pulse prior to forminga plasma sheath.

In embodiments of the present technology, the pulsed DC potential may beinitiated to prime the plasma, and then cycled off to prevent theformation of a high-voltage DC plasma sheath at the substrate surface.Thus, conventional DC bias maintains the pulse long enough to develop asheath, which is at a high voltage and affects the ion energies. Thepresent technology may utilize the pulsed DC power to create primingparticles to allow a low RF power to ignite a plasma each time it ispulsed on. The low RF power, which may be below a typical breakdownvoltage, provides lower ion energies than would be produced in ahigh-voltage DC plasma sheath, such as produced by a conventional DCbias. The pulsed DC power of the present technology instead produces thepriming particles that allow avalanche breakdown and development of thesheath when the RF bias cycles on, despite the low power of the RF bias.The result is a plasma sheath at lower ion energies, which may reduce orsubstantially reduce sputtering over conventional technologies. Byreducing the sputtering, higher selectivity may be afforded aspreviously explained.

To produce the functionality of the pulsed DC power, the duty cycle ofthe pulsed DC power may be very low, and may be associated with an ontime of 1 microsecond to about 100 microseconds in embodiments. Inembodiments the on time may be less than about 75 microseconds, lessthan about 50 microseconds, less than about 30 microseconds, less thanabout 25 microseconds, less than about 20 microseconds, less than about15 microseconds, less than about 10 microseconds, less than about 5microseconds, or less than about 1 microsecond.

In terms of duty cycle, while conventional DC bias may include a dutycycle of above 50%, above 75%, or above 90% in order to generate aplasma sheath, the present technology may utilize a duty cycle of thepulsed DC power that is less than about 50% in embodiments. The dutycycle of the pulsed DC power may also be less than about 40%, less thanabout 30%, less than about 25%, less than about 20%, less than about15%, less than about 10%, less than about 5%, or less than about 1% inembodiments. The DC power may also be pulsed at a duty cycle betweenabout 1% and about 50%, between about 1% and about 25%, between about 1%and about 10%, or any other range between or within these values.

The pulsed DC power may also be operated on an alternating orsemi-alternating frequency with the RF bias pulsing. For example, thefrequency of the pulsed DC power may be such that it is in the on cyclewhile the RF bias is in the off cycle and vice versa. Depending on theduty cycles of the two powers, either one of the two powers may beoperating at a given time or neither of the two powers may be operatingat a given time. In embodiments both may also be operating at a giventime. By utilizing the reduced duty cycles of the present technology, aplasma sheath may not be formed at the substrate surface while thepulsed DC power is operating. Thus, the pulsed DC power maintainspriming particles available for discharge breakdown and to stabilize theimpedance to improve the operating conditions of the system, while notforming a sheath or breakdown until the RF power is cycled on. In thisway, a variety of pressure ranges may be accommodated by the presenttechnology including pressure regimes below about 50 mTorr as well aspressure regimes up to several hundred mTorr or above. Put another way,the present technology controls the impedance for glow dischargebreakdown to remove the conventional impedance limitations ofconfiguration, orientation, pressure, chemistry, etc.

The pulsed DC power may be coupled with the system in a number of waysfurther described below in relation to the other figures. For example,and as described in detail below, the pulsed DC power may be applied toa bipolar electrostatic chuck supporting the semiconductor substrate.Additionally, the pulsed DC power may be applied to a conductive ringembedded in or coupled with a shield ring of a pedestal supporting thesemiconductor substrate. Still further, the pulsed DC power may beapplied to a conductive ring embedded in or connected with a showerheadwithin the processing chamber.

Turning to FIG. 2 is shown a graph illustrating the additive effects ofmaterial modification and low-power plasma according to embodiments ofthe present technology. As illustrated, an exemplary process may includeremoving an oxide film relative to a carbide film on the surface of asubstrate. As shown by the first bar, a reactive-ion etching orcontinuous waveform process may provide a selectivity below 10:1 for theoxide material with respect to the carbide material. This may be due inpart to the sputtering caused by the ion process, which is moreaggressive to all materials thereby increasing both etch rates.Moreover, the reactive-ion etch may also produce rounded corners in theetch profile and may also etch an underlying layer due to ionbombardment once the desired film has been removed. Accordingly, areactive-ion etch may be unsatisfactory for selective processing andmaintaining features of the substrate.

As shown in the second bar, by simply utilizing the pulsing low-power RFbias plasma described above, such as with the pulsed DC power,selectivity may be improved over the conventional reactive-ion etchprocess. The process may also reduce or eliminate the corner roundingand underlying layer etch produced by reactive-ion etching. The thirdbar, however, illustrates the synergistic benefits of performing amaterial modification prior to performing the low-power pulsing. Byutilizing both film modification as well as the low-power plasma RFpulsing process, selectivity increases by almost an order of magnitudeover the reactive-ion etching process. Additionally, the etch profile ismuch improved with reduced corner rounding and underlying layer etching.

FIG. 3 illustrates imaging of an etch process performed according toembodiments of the present technology. As shown in the image on theleft, regions of silicon nitride 305 are disposed between regions ofsilicon carbide 310. After a material modification and low-power RFetching operation as previously discussed are performed, the siliconcarbide sections are removed, as illustrated in the figure on the right.The layers of silicon nitride 305 are substantially maintained, and onlyminimal corner rounding can be observed. Additionally, silicon oxidelayer 315 underlying the silicon carbide sections 310 was exposed duringthe etch process, but the film was able to act as an etch stop to theprocess, as opposed to a reactive-ion process that would have etchedinto the trench due to bombardment of the silicon oxide. The measuredeffects illustrate that the present technology was able to produce anetch selectivity of silicon carbide to silicon nitride of over 50:1 withminimal corner rounding of the silicon nitride. The present technologywas also able to produce an etch selectivity of silicon carbide tosilicon oxide of over 70:1.

FIG. 4 shows a chart illustrating etch rates of various materials withand without a treatment according to embodiments of the presenttechnology. The present example shows a material modification thatutilized an oxygen precursor in plasma to modify silicon oxycarbide,silicon oxide, silicon carbide, and silicon nitride exposed on asubstrate surface. A low-power pulsed RF etching process was performedon similar materials with and without the oxygen treatment. Asillustrated, all four films etched with low selectivity during thelow-power etch process without the material modification. On the otherhand, after the oxygen treatment, silicon oxycarbide and silicon carbidecontinued to etch, while the silicon oxide and silicon nitride filmswere essentially maintained and buffered by the oxygen treatmentproviding a surface enhancement to those films.

FIG. 5 shows a chart illustrating etch rates of silicon oxycarbide andsilicon carbide with and without treatments according to embodiments ofthe present technology. Although the oxygen modification performed inthe example illustrated in FIG. 4 was successful for thecarbon-containing films with respect to silicon oxide and siliconnitride, the two carbon-containing films did not have high selectivitywith respect to each other. In FIG. 5, a physical modification wasperformed that exploited the higher porosity of the silicon oxycarbidefilm. Silicon oxycarbide is a more porous film than silicon carbide, andthe chemical bonding is weaker as well. The physical modification ofthis example included utilizing a helium precursor in plasma, and thenexposing the films to those plasma effluents. Because helium is inert tothe two films, it did not chemically react with the materials, althoughthe impact of the helium ions was of a sufficient capacity to damage thechemical bonds of the silicon oxycarbide. This further weakened thefilm, after which a low-power RF pulsing etch was performed. Asillustrated by the figure, the modification followed by the low-poweretch removed the silicon oxycarbide material while essentiallymaintaining the silicon carbide.

The examples illustrated by FIGS. 4 and 5 are exemplary only, and arenot intended to limit the present technology. These examples merely showthe types of material modifications encompassed by the presenttechnology. One of skill will readily understand by these examples howthe material modifications and low-power etch operations may be appliedto a variety of materials to enhance selectivity and improve etchprofiles. By utilizing the present technology, greater than 20:1selectivity may be achieved for silicon oxycarbide with respect tosilicon oxide and silicon nitride. Greater than 20:1 selectivity mayalso be achieved for silicon oxide with respect to silicon oxycarbide,silicon nitride, and silicon carbide using various materialmodifications and etching according to the present technology. Greaterthan 20:1 selectivity may also be achieve for silicon carbide withrespect to silicon oxide, silicon nitride, and silicon oxycarbide usingvarious material modifications and etching according to the presenttechnology. Additionally, greater than 20:1 selectivity may be achievedfor silicon nitride with respect to silicon oxide, silicon oxycarbide,and silicon carbide using various material modifications and etchingaccording to the present technology. In embodiments the selectivity ofany of these operations may also be greater than or about 25:1, greaterthan or about 30:1, greater than or about 35:1, greater than or about40:1, greater than or about 45:1, greater than or about 50:1, greaterthan or about 55:1, greater than or about 60:1, greater than or about65:1, greater than or about 70:1, greater than or about 75:1, greaterthan or about 80:1, greater than or about 85:1, greater than or about90:1, greater than or about 95:1, or greater than or about 100:1.

Turning to FIG. 6 is shown a partial schematic illustration of acontroller providing DC pulse to an electrostatic chuck according toembodiments of the present technology. The system may be included with asubstrate processing chamber according to embodiments of the presenttechnology. An exemplary chamber may be the Mesa™ Etch System producedby Applied Materials, Inc. of Santa Clara, Calif. The components mayinclude a pedestal 605 configured to support a semiconductor substrate.The system may also include a pulsed RF bias power 610 electricallycoupled with the pedestal and configured to generate a plasma aspreviously described. The pulsed RF bias power 610 may be configured togenerate a plasma within the processing chamber at a power of betweenabout 20 W and about 50 W, and the pulsed RF bias power may be pulsed ata frequency below about 5,000 Hz. The system may also be configured tooperate at any of the other levels previously described.

The system may also include a DC pulsing power 615 electrically coupledwith the substrate processing chamber. The DC pulsing power 615 may beas previously described, and configured to produce priming particles forthe RF bias plasma. In embodiments, the DC pulsing power may beconfigured to pulse at a frequency to produce priming particles withoutdeveloping a plasma sheath. The DC pulsing power may be operated for anyof the times or at any of the duty cycles previously described, and maybe configured to be pulsed for a duration of 100 microseconds or less ata duty cycle of less than about 50%. The DC pulsing power may also beconfigured to be operated for a pulse duration of less than about 50microseconds at a duty cycle of less than about 20%. The DC pulsingpower may also be configured to be operated for a pulse duration of lessthan about 10 microseconds at a duty cycle of less than about 10% inembodiments.

As illustrated in FIG. 6, the pedestal 605 may be an electrostaticchuck. A chamber controller 620 may provide instructions to theelectrostatic chuck controller 625, including the input/output module630 for the bipolar electrostatic chuck. The DC pulsing power 615 may beelectrically coupled with electrical ground of the bipolar electrostaticchuck 630 as illustrated in the figure. In many processing chambers theelectrodes may be biased to DC voltages, and heavy filtering may beincluded at the output of the DC power supplies to block RF power.Consequently, when the supplies are pulsed as shown in theconfiguration, the waveform may begin to be distorted and attenuated.Accordingly, to overcome this issue, the electrostatic chuck power maybe floated at the voltage of the pulsed DC. Thus, the electrostaticchuck electrodes are then referenced to the high voltage of the pulsedDC. Put another way, the electrostatic chuck power supply may then befloating electrically isolated from the machine ground, and ground ofthe electrostatic chuck essentially may be at high voltage. Theelectrostatic chuck can then output positive and negative polarity withrespect to the high voltage.

Thus, if the pulsed DC is cycled off or grounded, then the electrostaticchuck electrodes would be referenced to the ground, plus or minus.However, when the DC is applied or pulsed, then the electrostatic chuckelectrodes would be referenced to the power of the applied DC power. Asa non-limiting example of such a configuration for the purposes ofexplanation, and not as a particular process scenario, if the pulsed DCpower operates at 1 kV, and the electrostatic chuck operates at +/−500volts, when the DC power supply is cycled on to assist with plasmageneration as previously described, then the electrodes would be at 1500volts and 500 volts respectively. A benefit of this configuration may bethat an additional conductor for the pulsed DC power may not be requiredinside the chamber. Additionally, in embodiments the DC and RF pulsesmay be alternated, and thus the DC and RF supplies may be decoupled fromone another despite that they are each biasing the same pedestal base.

An additional coupling option that may be decoupled from theelectrostatic chuck is illustrated in FIG. 7, which shows a partialschematic illustration of a controller providing DC pulse to a conductorcoupled with a pedestal structure according to embodiments of thepresent technology. As illustrated in the figure, a substrate processingchamber 701 is shown having a showerhead 703 and a pedestal 705configured to support a substrate. The system may include a pulsed RFbias 710 as previously discussed, as well as a DC power 715 forelectrostatic chucking. An additional DC pulsing unit 720 may beincluded that provides pulsed DC power as previously discussed forproducing priming for a plasma ignited by the RF bias. In this example,the DC pulsing power is electrically coupled with a conductive ring 725embedded in or coupled with the pedestal. This conductive ring 725 maybe decoupled from the electrostatic chuck and from the RF bias inembodiments. For example, the conductive ring 725 may be included in adielectric shield ring, including a quartz shield ring of the pedestal705 as shown. The conductive ring may be any conductive materialincluding a metal or silicon carbide in embodiments. In this scenario,although an additional conductor is included in the system, because theconductive ring is decoupled from the other power supplies, thecomponents do not require electrical floating with respect to oneanother.

Another coupling option that may be decoupled from the electrostaticchuck is illustrated in FIG. 8, which shows a partial schematicillustration of a controller providing DC pulse to an embedded conductorwithin a showerhead of a processing chamber according to embodiments ofthe present technology. As illustrated, components similar to thosediscussed with respect to FIG. 7 are shown, including a substrateprocessing chamber 701, including showerhead 703, and pedestal 705, forexample. The system similarly includes a pulsed RF bias 710, a DC power715 for electrostatic chucking, and a DC pulsing unit 720. The figureadditionally includes a conductive ring 825 which may be a similarmaterial as discussed above, but may be coupled with showerhead 703 inembodiments. This coupling option also decouples the pulsed DC from theother power supplies.

The coupling ring may also be included coupled with or embedded in achamber wall in embodiments, or other components of the chamber system.By providing the pulsed DC power with any of these options oralternative options as would be readily understood to be similarlyencompassed, the system may produce lower power plasma than conventionalsystems. By providing energy to produce energetic particles allowing thelow-power, pulsing RF bias to more easily strike a plasma at lowervoltages with lower ion energies, improved plasma processing may beprovided for etching, deposition, cleaning, or any other process thatmay benefit from a low-power plasma.

In the preceding description, for the purposes of explanation, numerousdetails have been set forth in order to provide an understanding ofvarious embodiments of the present technology. It will be apparent toone skilled in the art, however, that certain embodiments may bepracticed without some of these details, or with additional details.

Having disclosed several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theembodiments. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent technology. Accordingly, the above description should not betaken as limiting the scope of the technology.

Where a range of values is provided, it is understood that eachintervening value, to the smallest fraction of the unit of the lowerlimit, unless the context clearly dictates otherwise, between the upperand lower limits of that range is also specifically disclosed. Anynarrower range between any stated values or unstated intervening valuesin a stated range and any other stated or intervening value in thatstated range is encompassed. The upper and lower limits of those smallerranges may independently be included or excluded in the range, and eachrange where either, neither, or both limits are included in the smallerranges is also encompassed within the technology, subject to anyspecifically excluded limit in the stated range. Where the stated rangeincludes one or both of the limits, ranges excluding either or both ofthose included limits are also included. Where multiple values areprovided in a list, any range encompassing or based on any of thosevalues is similarly specifically disclosed.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural references unless the context clearly dictatesotherwise. Thus, for example, reference to “a material” includes aplurality of such materials, and reference to “the precursor” includesreference to one or more precursors and equivalents thereof known tothose skilled in the art, and so forth.

Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”,“include(s)”, and “including”, when used in this specification and inthe following claims, are intended to specify the presence of statedfeatures, integers, components, or operations, but they do not precludethe presence or addition of one or more other features, integers,components, operations, acts, or groups.

What is claimed is:
 1. A method of performing a selective etch, themethod comprising: modifying a material on a semiconductor substratehaving at least two exposed materials on a surface of the semiconductorsubstrate; forming a low-power plasma within a processing chamberhousing the semiconductor substrate, wherein the low-power plasma is aradio-frequency (RF) plasma, and wherein the low-power plasma is atleast partially formed by an RF bias power operating at between about 10W and 100 W and at a pulsing frequency below about 5,000 Hz; and etchingone of the at least two exposed materials on the surface of thesemiconductor substrate at a higher rate than a second of the at leasttwo exposed materials on the surface of the semiconductor substrate. 2.The method of claim 1, wherein the modifying comprises forming a plasmafrom a precursor within the processing chamber with the RF bias power.3. The method of claim 2, wherein the precursor is selected from thegroup consisting of oxygen, hydrogen, or helium.
 4. The method of claim1, wherein each of the at least two exposed materials on the surface ofthe semiconductor substrate are selected from the group consisting ofsilicon oxide, silicon nitride, silicon carbide, and silicon oxycarbide.5. The method of claim 1, wherein the RF bias power at least partiallyforming the low-power plasma operates at a duty cycle below about 50%.6. The method of claim 1, wherein forming the low-power plasma furthercomprises utilizing an RF source power below about 100 W.
 7. The methodof claim 1, wherein forming the low-power plasma further comprisesutilizing a pulsed DC power.
 8. The method of claim 7, wherein thepulsed DC power is applied to a bipolar electrostatic chuck supportingthe semiconductor substrate.
 9. The method of claim 7, wherein thepulsed DC power is applied to a conductive ring embedded in a shieldring of a pedestal supporting the semiconductor substrate or embedded ina showerhead within the processing chamber.
 10. A method of removingmaterial from a semiconductor substrate, the method comprising:modifying a material on a semiconductor substrate having at least twoexposed materials on a surface of the semiconductor substrate, whereinthe modifying comprises forming a plasma from a precursor with an RFbias power to generate plasma effluents that modify the material;forming a low-power plasma within a processing chamber housing thesemiconductor substrate, wherein the low-power plasma is aradio-frequency (RF) plasma, and wherein the low-power plasma is formedby a pulsed RF bias power operating at between about 20 W and 50 W at apulsing frequency between about 500 Hz and about 2,000 Hz at a dutycycle of between about 20% and 50%; operating a DC pulsed power on analternating frequency with the RF bias power pulsing; and etching one ofthe at least two exposed materials on the surface of the semiconductorsubstrate at a selectivity of at least about 20:1 with respect to asecond of the at least two exposed materials on the surface of thesemiconductor substrate.
 11. The method of claim 10, wherein themodifying comprises a chemical modification causing a chemical change tothe material on the semiconductor substrate.
 12. The method of claim 10,wherein the modifying comprises a physical modification utilizing aninert precursor.
 13. The method of claim 12, wherein the physicalmodification comprises damaging bonds of the material on thesemiconductor substrate with ions of the inert precursor.
 14. The methodof claim 10, wherein forming the low-power plasma further comprisesutilizing an RF source power operating up to about 100 W.